This is great. I wonder if it would be easier to start by cutting the dowel in half. Then slicing the halves into disks using a stop block. I guess alignment when gluing back together would be difficult.

Yes, but you're also missing some of the features of the end tab of a tape measure by doing this. It usually has a little wiggle and that is to account for the width of the tab when measuring inside vs outside objects. This is an interesting idea, but as others point out, it takes a multi-function tool and makes it a single function tool.